The design of bus controllers has evolved over the years as performance requirements and customer needs have driven computer architectures to become more sophisticated and efficient. Specifically, the desire for higher performance has necessitated that a bus controller be able to operate with both a local bus and a system bus simultaneously and autonomously. Additionally, a bus controller that is not limited with regard to speed is needed; in this way both the local bus or the system bus may interact with the bus controller as fast as circuitry on the boards permit without suffering from speed limitations incurred by the bus controller. Lastly, a need has been felt for a bus controller that may operate as a master during a transaction or as a slave during a transaction simultaneously with both the local bus and the system bus, thus providing for more system flexibility.
The design of bus architectures typically include a number of compromises to optimize performance parameters that may be inversely related to one another. Certain bus architecture standards are designed as open standards to provide a general framework, yet provide flexibility so that performance criteria may be enhanced for specific system applications. Futurebus+ is one such open standard. The Futurebus+ standard is an IEEE specification #896.1-1991 and is described in an article entitled "Futurebus+ Coming of Age" (Theus, John, "Futurebus+ Coming of Age", Microprocessor Report, May 27, 1992, pp. 17-22).
It is an object of this invention to provide a dual bus controller architecture that enables simultaneous, autonomous interaction with both the local bus and the system bus and is compatible with the Futurebus+ bus architecture standard (IEEE spec #896.1-1991). It is another object of this invention to provide a dual bus controller architecture that allows both the local bus and the system bus to interact with the bus controller operating as a master or a slave without any imposed speed limitations. Other objects and advantages of the invention will become apparent to those of ordinary skill in the art having reference to the following specification together with the drawings herein.